Blackphone, launched in February this year, features PrivatOS, a privacy-enhanced operating system built on Android. The smarphone's OS and apps are claimed to ensure that conversations and messages are not vulnerable to hackers or government surveillance.

The private mobile is scheduled to be shipped from June, and the company says the fresh capital will enable it to meet the "overwhelming demand for Blackphone".

"With a customer base including consumers in over 130 countries, 23 of the global Fortune 50 enterprises and governments from 11 nations - we now have the resources to meet the demand for our encrypted mobile voice, video, secure file transfer and international secure calling plans - all available for iOS and Android."